[关键词]
[摘要]
对甘肃省灵台县独店镇秋射村黄土剖面浅层地下水的水化学组成、溶解无机碳(DIC)、溶解有机碳(DOC)、颗粒有机碳(POC)等进行了取样分析,对其δ13CDIC和 δ13CPOC的特征及其控制因素进行了探讨,并评估了降雨补给过程中的碳酸盐风化碳汇强度。结果表明,研究区地下水的水化学类型为HCO3-Ca?Mg型,其方解石饱和指数SIC大于0,已经饱和,但尚未达到大规模沉淀的程度。研究区黄土浅层地下水的DIC变化范围为5.25~5.45 mmol/L,DOC含量为0.59~0.62 mg/L,明显低于地表水体;而POC稍高,这是因为黄土颗粒物的混入造成。泉水和井水的δ13CDIC变化范围在-9.19‰~-8.90‰之间,其较高的δ13C与碳酸盐风化-沉积过程中反复的碳同位素交换有关。而δ13CPOC变化范围在-19.99~-18.87‰之间,与黄土有机碳同位素特征基本一致。地下水中的HCO3-、Ca2+和Mg2+主要来源于碳酸盐的化学风化。根据风化反应的离子平衡关系,计算得到研究区的风化碳汇为2.82mmol/L,即每有1L的降水入渗到零通量面以下,就会产生2.82mmol的碳汇。
[Key word]
[Abstract]
The hydro-chemical composition, Dissolved Inorganic Carbon (DIC), Dissolved Organic Carbon (DOC), Particulate Organic Carbon (POC) and δ13CDIC, δ13CPOC in spring water discharging from loess section in Qiushe village, Dudian town, Lingtai county, Gansu province of Northwestern China were determined, and CO2 consumption of carbonate weathering during rainfall recharge was estimated in this study. The results show that the chemical type of groundwater in study area is HCO3-Ca?Mg type. The Saturation Index of calcite (SIc) in spring water (above 0) displays the springs are saturated, however, the spring hardly appears the phenomenon of massive precipitation. The DIC concentration in groundwater of loess area is 5.25~5.45mmol/L, and the DOC concentration is 0.59 ~ 0.62 mg/L, lower than that in surface water. While POC concentration is high due to the mixture of loess particle matter. The δ13C of DIC in springs and wells ranged from -9.19‰ to -8.90‰. The positive distribution of δ13CDIC may be attributed to the repeated exchange of C isotope during the process of carbonate weathering and precipitation. The δ13CPOC ranged from -19.99‰ ~ -18.87‰, consistent with the isotope ratio of the organic carbon in loess. The HCO3-, Ca2+ and Mg2+ in groundwater mainly derive from the weathering of carbonate in loess. According to the ion balance of carbonate weathering reaction, the CO2 sink by carbonate weathering is calculated up to 2.82mmol/L. In other words, the 2.82mmol CO2 can be absorbed by carbonate weathering when 1 L rainfall can infiltrate into the loess until below the zero flux plane.
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[基金项目]
自然科学基金项目(41403107; 41325010);地科院水环所基本科研业务费项目(SK201208);中国地质调查项目(12120113005900)